EP0947835A2 - Micromechanical component having a moving dielectric element and a method of manufacture - Google Patents

Abstract

The component has a fixed micromechanical structure incorporating a pair of capacitor plates (K) and a relatively movable micromechanical structure provided by a dielectric layer (4), its movement causing a variation in the capacitance between the capacitor plates. The movable micromechanical structure may be freely movable, or spring-loaded for displacement into the space between the capacitor plates provided by respective conductive layers (2, 7), separated by intermediate insulating layers (3, 5).

Description

The invention relates to a microsystem on a Semiconductor substrate with an integrated circuit and a micromechanical component, the micromechanical component a fixed micromechanical structure and a movable one micromechanical structure includes, as well as a Manufacturing process.

Micromechanical components are used for various purposes used, an important area of application is proportional and non-proportional force sensors (acceleration and Inclination sensors). The known sensors of this type have fixed and mobile micromechanical structures and are based on the capacitive measurement of the variation of the Electrode gap of a micromechanical capacitor. E.g. is described in the article by Sherman et al., Conf. Proc. IEDM 1992, p.501 (No. 0-7803-0817-4 / 92 IEEE) a structure proposed in which a movably suspended Polysilicon tongue between two fixed tongues located. An acceleration changes the distance of the movable tongue relative to the fixed tongues, causing the Capacity increases to one of the fixed tongues and to the other decreases. This change is detected electrically.

In the manufacture of such micromechanical components there is a lot of interest in processes related to Manufacturing of integrated circuits, especially on a silicon substrate. Just one Compatibility of the manufacturing processes allows integration of micromechanics and control or evaluation circuits in microsystems. This is also important if existing semiconductor manufacturing systems also for manufacturing can be used by micromechanical structures should. A process with which an integrated circuit and a micromechanical at the same time Component in different areas of the semiconductor substrate generated, i.e. a microsystem with only minimal additional process effort for integrated Circuit is established.

a) Polysilizium Center-pin- und Flange-Prozeß (M. Mehrengany, Y.-C. Tai, J. Micromech. Microeng., vol. 1, 73, 1991) Dieser Prozeß erfordert bei der Herstellung der mikromechanischen Strukturen im Anschluß an die Herstellung der integrierten Schaltung zusätzliche Polysiliziumabscheidungen nach dem Metallisierungskomplex. Im Fall, daß der Center-Pin-Prozeß vor der Metallisierung der integrierten Schaltung durchgeführt werden soll, ergibt sich das Problem, die beweglichen Strukturen freizuätzen, und gleichzeitig die Isolation der Metallisierung zu schützen. Ein weiterer Nachteil ist der relativ hohe spezifische Widerstand von dotiertem Polysilizium.

b) Polysilizium LOCOS-Prozeß (L.S. Tavrow et al, Sensors and Actuators A, Phys. vol. A35, 33, 1992):
Der Prozeß sieht vor, die beweglichen mikromechanischen Strukturen auf einer planen LOCOS-Oxidschicht herzustellen, wobei der Oxidationsschritt wegen der Temperaturbelastung nur vor der Transistorherstellung einer integrierten Schaltung erfolgen kann. Bei vollständiger Durchführung des Prozesses vor Herstellung der integrierten Schaltung ergibt sich eine ungünstige Topologie für die Nachfolgeschritte sowie das Problem, die mikromechanischen Strukturen während der Herstellung der integrierten Schaltung zu schützen. Bei einer ineinander verzahnten Herstellung muß das Problem der Freiätzung des Rotors bei gleichzeitigem Schutz der Schaltungsisolationsoxide gelöst werden.

c) Selektiver Wolfram-Prozeß (L.Y.Chen et al, TRANSDUCERS '91., Int. Conf. on Solid-State Sensors and Actuators. San Francisco, USA, IEEE Cat. No. 91CH2817-5, 739, 1991):
Dieser Prozeß kann im Anschluß an einen Schaltungs-Fertigungsprozeß durchgeführt werden, wobei das Problem der elektrischen Kontaktierung und des Schutzes der Metallisierungsisolation durch das vorgeschlagene Verfahren nicht gelöst werden. Der Prozeß ist insbesondere bezüglich der Lithographieschritte sehr aufwendig.

d) LIGA-Prozeß (P.Bley et al, Microelectronic Engineering 13, 509, 1991; H. Guckel et al, Conf. Proceedings IEEEMicro Electro Mechanical Systems, Nara, Japan, 1991): Dieser Prozeß benötigt Röntgenstrahl-Lithographie und eventuell eine nachträgliche Montage von losen mikroskopischen Bauteilen.

The following manufacturing processes are known for micromechanical components:

a) Polysilicon center-pin and flange process (M. Mehrengany, Y.-C. Tai, J. Micromech. Microeng., vol. 1, 73, 1991) This process requires subsequent to the manufacture of the micromechanical structures the manufacture of the integrated circuit additional polysilicon deposits after the metallization complex. In the event that the center pin process is to be carried out before the metallization of the integrated circuit, the problem arises of freeing out the movable structures and at the same time protecting the insulation of the metallization. Another disadvantage is the relatively high specific resistance of doped polysilicon.

b) Polysilicon LOCOS process (LS Tavrow et al, Sensors and Actuators A, Phys. vol. A35, 33, 1992):
The process provides for the movable micromechanical structures to be produced on a flat LOCOS oxide layer, the oxidation step being able to take place only before the transistor production of an integrated circuit due to the temperature load. When the process is completely carried out before the integrated circuit is manufactured, there is an unfavorable topology for the subsequent steps and the problem of protecting the micromechanical structures during the manufacture of the integrated circuit. In the case of an interlocking production, the problem of free etching of the rotor while protecting the circuit insulation oxides must be solved.

c) Selective tungsten process (LYChen et al, TRANSDUCERS '91., Int. Conf. on Solid-State Sensors and Actuators. San Francisco, USA, IEEE Cat. No. 91CH2817-5, 739, 1991):
This process can be carried out after a circuit manufacturing process, the problem of electrical contacting and protection of the metallization insulation not being solved by the proposed method. The process is very complex, particularly with regard to the lithography steps.

d) LIGA process (P.Bley et al, Microelectronic Engineering 13, 509, 1991; H. Guckel et al, Conf. Proceedings IEEEMicro Electro Mechanical Systems, Nara, Japan, 1991): This process requires X-ray lithography and possibly one subsequent assembly of loose microscopic components.

All of these processes are not designed for you joint and in particular simultaneous production of integrated circuit and the micromechanical component in a microsystem. You need a variety of Layers and process steps, which exclusively the Production of the micromechanical component and serve for the manufacture of an integrated circuit is unnecessary or are even restrictive or disadvantageous.

The invention is therefore based on the object of a novel Concept for a microsystem with a micromechanical Specify component, the component as a motor, actuator or Force sensor can be used, as well as a Specify manufacturing process for a microsystem in which based on the IS production a minimal additional process effort for the production of micromechanical component is necessary.

This object is achieved by the features of claims 1 and 10 solved.

The invention is based on the combination of one micromechanical component, which is a dielectric movable Structure and one of one or more conductive layers formed pair of capacitor plates, and one integrated circuit, the circuit elements of which using the conductive layer or layers are wired. The dielectric movable structure is between the Capacitor plate pair movable. The micromechanical Component can in particular be a motor with a dielectric Represent rotor or a force sensor.

When used as a force sensor, the dielectric becomes movable Structure by the force to be measured between the Capacitor plate pair introduced, so that its capacity changes. The change in capacity is measured. Vice versa the force can also remove the dielectric from the Cause space. The dielectric structure can be free or be resiliently movable, so that the component is a non-proportional or a proportional force sensor represents. The component principle can also be used for actuators be used because the field of a charged capacitor exerts a force on the dielectric. In any case, is a Material with high dielectric constant εr advantageous, e.g. e.g. Silicon nitride.

In the manufacturing method according to the invention, the pair of capacitor plates from the same or from different conductive layers that are ready for wiring the Integrated circuit of the microsystem are needed structured. The moveable structure becomes a structured dielectric layer. Fixed and agile Structures are made with an insulating layer separated from each other. Then a mask is applied and performed an etching process with an isotropic component, of the insulating layer at least around the dielectric around selectively removed to the solid structure. After the etching process the dielectric can move freely or resiliently. With a freely movable micromechanical structure these no longer have any connection to the rest after the etching process Component. With a resiliently movable micromechanical Structure still has a connection, namely preferably over a part of the side led out dielectric layer with a small cross-sectional area, the on its other side e.g. with a mounting plate is connected and as a spring element between movable Structure and mounting plate works.

The process can be proportional or non-proportional Force sensor or a motor with dielectric Rotor are manufactured. In the first case they are preferred superimposed conductive layers for the capacitor plate pair used so that it essentially is arranged parallel to the substrate surface. Between a lower insulating layer is located in the conductive layers Layer, the dielectric layer and an upper insulating Layer. In the latter case, one or more Capacitor plate pairs preferably made of the same conductive Structured layer, the insulating and the dielectric Layer applied and the dielectric layer to an im Free space between the plates (after the etching process) Structure structured; the dielectric structure can also be made in front of the capacitor plates. A non-proportional Sensor can be used with both depending on the requirement Concepts can be realized.

In the microsystem according to the invention, one or several conductive layers that are already used for wiring of the integrated circuit are required as parts of the micromechanical component used. This layer or Layers only have to be designed accordingly be structured that in the field of micromechanical Component a pair of capacitor plates as a fixed micromechanical Structure is formed. The manufacture of the dielectric Structure is generally in one for IS production additional process step, the isotropic etching process at the IS production already for the free etching of the connection pads needed. The integrated circuit can be a single or Multi-layer wiring (i.e. one or more Metallization levels), one or more of which or all can be used for the micromechanical component can. Furthermore, the integrated circuit in one any technology, for example CMOS.

FIG 1 - 2

einen Querschnitt durch ein Halbleitersubstrat im Bereich des mikromechanischen Bauteils des Mikrosystems, an dem das Verfahren verdeutlicht wird,

FIG 3

eine Aufsicht auf das mikromechanische Bauteil aus FIG 1

FIG 4 - 6

einen Querschnitt durch bzw. eine Aufsicht auf ein mikromechanisches Bauteil des Mikrosystems gemäß einer weiteren Ausführungsform der Erfindung.

The invention is explained in more detail below on the basis of exemplary embodiments which are illustrated in the figures. Show it:

FIG 1-2

3 shows a cross section through a semiconductor substrate in the region of the micromechanical component of the microsystem, on which the method is illustrated,

FIG 3

a top view of the micromechanical component from FIG. 1

FIG 4-6

a cross section through or a plan view of a micromechanical component of the microsystem according to a further embodiment of the invention.

FIG 1-3:

The first exemplary embodiment is a microsystem described, in which the micromechanical component as a non-proportional Force sensor can be used. The Micromechanical component has an essentially parallel to the substrate surface (horizontally) Capacitor plate pair formed from the conductive layers 2 and 7, as a fixed micromechanical component and an im essential horizontally movable dielectric 4 as free movable micromechanical component. preferably that is Dielectric ring-shaped and with a fuse provided against falling out from the upper conductive Layer can be formed.

1 shows a substrate 1 with any surface (e.g. Silicon or a field oxide). On the substrate a lower conductive layer 2, for example a Polysilicon layer or a first metallization level, applied and structured. The lower conductive layer 2 is covered with a lower insulating layer 3, a dielectric layer 4 is applied thereon and structured to the moving structure. It will be one Upper insulating layer 5 applied and possibly with contact holes provided with a suitable material to be filled up to contacts 6. These serve in the BT area Contacts for the production of the (mechanical) fuse, so that their electrical resistance is immaterial here. On the upper insulating layer 5 becomes the upper conductive Layer 7 applied and structured so that it in a predetermined area a pair of capacitor plates with the forms lower conductive layer 2, so this partially overlaps. In the area of the integrated circuit of the Microsystems serve the lower and the upper conductive layer the wiring. The dielectric 4 is structured in such a way that it (after the isotropic etching process) in the space insertable from the capacitor plates or out of it is removable. A layer 7 can also be used Protection against falling out of the later to be exposed movable structures are formed, for example by a closed bracket with the help of the underlying Layers (s.FIG 3) is formed, or by placing on the contact 6 an area is formed which has a larger diameter than the corresponding inner diameter of the annular Dielectric 4 has. The top conductive layer is covered with another insulation 8 (passivation) covered.

• Der Ätzprozeß muß ausreichend selektiv zum Dielektrikum 4, den leitenden Schichten 2, 7 und in diesem Beispiel auch zum Kontakt 6 sein,
• die isotrope Komponente des Ätzprozesses und die Größe der Öffnung in der Maske müssen unter Berücksichtigung der einzelnen Schichtdicken so gewählt sein, daß das Dielektrikum 4 völlig unterätzt wird. Der Plattenzwi schenraum muß ebenfalls weit genug freigeätzt sein.

A mask 9 is applied, which has an opening in the BT region above the movable structure 4 to be exposed, then the insulating layers 3, 5, 8 are etched. The following conditions must be taken into account:

• The etching process must be sufficiently selective for the dielectric 4, the conductive layers 2, 7 and in this example also for the contact 6,
• The isotropic component of the etching process and the size of the opening in the mask must be chosen taking into account the individual layer thicknesses so that the dielectric 4 is completely under-etched. The plate interspace must also be etched free enough.

The etching process is preferably carried out as a wet etch with a buffered HF solution or as a microwave assisted Dry etching performed.

For the individual steps of the manufacturing process you can the processes and materials known from IS production (e.g. silicon oxide as insulating and Al alloys as conductive layer) can be used. For example, the Production of the metal level simultaneously with the Filling the contacts is done by after etching the Contact holes in the corresponding insulation layer Adhesive layer (for example 40nm Ti + 10Onm TiN) deposited and then in a CVD process tungsten for pad filling and at the same time as layers of metallization is applied.

• An dem Substrat 1 werden weitere, für die Herstellung der integrierten Schaltung notwendigen Verfahrensschritte vorgenommen, also beispielsweise Herstellen von epitaktischen Schichten, dotierten Wannen, Kanalimplantation, Gate-Oxid. Für die Gate-Ebene der IS kann die untere leitende Schicht 2 verwendet werden, für die Gate-Isolation (Zwischenoxid) bspw. die Schicht 3. Es wird u.a. eine Implantation der Source/Drain-Gebiete durchgeführt.
• Mithilfe der Kontakte 6 wird im IS-Bereich ein elektrischer Kontakt 6 der Metallisierungsebene 7 zur Gateebene 2 hergestellt.
  Im IS-Bereich dienen Kontakte 6 und die erste Metallisierungsebene beispielsweise auch zum Anschluß von S/D-Gebieten von Transistoren.
• Als isolierende Schichten werden vorzugsweise - in situ oder durch geeignete Prozesse - planare Schichten einge setzt. Planare Schichten sind auch im BT-Bereich vorteilhaft.
• Die weitere Isolation 8 besteht aus einer Passivierung aus Siliziumoxid und -nitrid.Die aufgebrachte Maske (9), die im BT-Bereich eine Öffnung oberhalb der freizulegenden beweglichen Struktur aufweist, besitzt im IS-Bereich oberhalb der von außen anzuschließenden Pads Öffnungen.

The component is integrated in a microsystem, the production of the IS (eg control or evaluation circuit in CMOS technology) taking place simultaneously with the process described. The following points are preferably taken into account:

• Further process steps necessary for the production of the integrated circuit are carried out on the substrate 1, that is to say, for example, production of epitaxial layers, doped wells, channel implantation, gate oxide. The lower conductive layer 2 can be used for the gate level of the IS, and layer 3 for the gate insulation (intermediate oxide), for example. The source / drain regions are implanted, among other things.
• With the help of the contacts 6, an electrical contact 6 of the metallization level 7 to the gate level 2 is produced in the IS area.
  In the IS area, contacts 6 and the first metallization level also serve, for example, for connecting S / D areas of transistors.
• As insulating layers, planar layers are preferably used - in situ or by suitable processes. Planar layers are also advantageous in the BT area.
• The further insulation 8 consists of a passivation of silicon oxide and nitride. The applied mask (9), which has an opening in the BT area above the movable structure to be exposed, has openings in the IS area above the pads to be connected from the outside.

In the IS area, the isotropic etching must be on these connection pads to stop.

A section of such an exemplary CMOS circuit is in German patent application DE OS 44 14 968 "Microsystem with integrated circuit and micromechanical component and manufacturing method "of the same Inventor and the same applicant in Figures 1 and 2 (with a 2-layer metallization) shown on the is referred to in this regard.

The microsystem can act as a non-proportional force sensor (Event sensor) can be used universally. So it can capacitively detected change in position of the ring also e.g. through the force of flowing media or direct mechanical effects are caused.

FIG 4 to 6:

• ein Kondensatorplattenpaar K, das aus einer oberen und einer unteren leitenden Schicht gebildet ist,
• ein Masse-Element M, das aus einer dielektrischen Schicht 4 gebildet, federnd aufgehängt und verschieden tief in den Plattenzwischenraum einführbar ist,
• ein Feder-Element F, welches auf einer Seite mit dem Masse-Element und auf der anderen Seite mit einer Befe stigungsplatte verbunden ist, und
• eine Befestigungsplatte B, die mit dem Substrat und dem Feder-Element verbunden ist.

A second example describes a microsystem with a micromechanical component that can be used as a proportional force sensor. It includes

• a capacitor plate pair K, which is formed from an upper and a lower conductive layer,
• a mass element M, which is formed from a dielectric layer 4, is suspended in a spring and can be inserted at different depths into the space between the plates,
• a spring element F, which is connected on one side to the mass element and on the other side to a fastening plate, and
• a mounting plate B, which is connected to the substrate and the spring element.

Preferably mass, spring and mounting plate are made the same layer. However, there may be some Tasks can also be advantageous, for example Spring element and mounting plate made of conductive layers to manufacture. The mounting plate and the Capacitor plates represent fixed micromechanical structures represents the mass element and the spring element (at least via a sufficient part) movable micromechanical Structures. The mounting plate does the job a mechanical connection of the spring element with the Substrate. The mounting plate B can also be omitted if it is ensured that the spring is sufficient largely not underestimated, but with the underlying insulating layer 3 mechanically connected remains. The capacitor plates K can be connected via lines L. be connected to an evaluation circuit.

The component can be used with the one described in the first example Processes are only made for the masks Structuring of the dielectric layer 4 and for the isotropic etching process (9) must be adapted. The Reference numbers for the individual layers correspond to those in Fig. 1-3. Since the movable element is not free is movable, the security against falling out is not provided and (in the area of the component) no contact 6 available.

The photomask 9 for the isotropic etching process has one sufficiently large opening so that, as already explained, at least the mass element M and one for the spring action sufficient part of the spring element F undercut be (FIG 6). Furthermore, there must be a sufficiently large space etched free between the capacitor plates 2.7 become. The mounting plate B is preferably not free or under-etched for secure mechanical attachment via the insulating layer 3 to the substrate 1 guarantee. 6, the etched-off area is 10 shown in dashed lines and designated 10. The insulating layers are not shown.

The capacitor plates can also lie essentially side by side formed from the same conductive layer be, and mass element M and spring element F can be so be formed between the plates that the mass in is movable substantially perpendicular to the substrate surface.

This component is like the first embodiment in one Integrated microsystem, the capacitor plates from the or the wiring level (s) are formed. The lines L can from a higher wiring level than the rest Structures are made.

If a force acts on the mass element, the spring F bends and the mass element changes its position. The change in location can be demonstrated as a change in capacitance (change in ε _r ) between the capacitor plates. Due to the restoring force of the spring, the capacity signal changes monotonically with the applied force. The component can therefore be used as an acceleration sensor by using the inertial force on the mass element. However, it is also possible to detect other forces acting on the mass element. For example, the force of a flowing liquid or gas or the direct force of an external mechanical component can be verified.

Furthermore, the component can be used as an actuator by putting a voltage between the capacitor plates creates. The electric field exerts a force on the mass element and causes a shift. In particular, can an AC voltage is also applied to the capacitor plates be, causing the dielectric mass element to Vibrations is excited (oscillator function). Since the mechanical vibration amplitudes when excited with the Spring mass system natural frequency become maximum, and one The component can lead to extreme values in AC resistance as a frequency-determining element in an electronic Circuit used (resonator).

Claims (13)

Microsystem on a semiconductor substrate (1) with a micromechanical component (BT) with a fixed micromechanical structure, which comprises a capacitor plate pair (K) formed from one or more conductive layers (2,7), and with a movable micromechanical structure, which is formed from a dielectric layer (4) and is movable in the space between the plates, and an integrated circuit (IS) with circuit elements which are wired using the conductive layer or at least one of the conductive layers (7). Microsystem according to claim 1, wherein the movable micromechanical structure is resiliently movable, and that Component a proportional force sensor, an actuator or represents an oscillator / resonator. Microsystem according to Claim 1, in which the movable micromechanical Structure is free to move. Microsystem according to Claim 3, in which the component (BT) represents a dielectric rotor motor. Microsystem according to claim 3, wherein the movable micromechanical Structure in the space between the plates is insertable or removable from it, and the component represents a non-proportional force sensor. Microsystem according to one of claims 1 to 5, wherein the integrated circuit (IS) in several conductive layers Form of a multilayer metallization and the solid micromechanical structures from several of the Metallization level are formed. Microsystem according to one of claims 1 to 6, wherein the integrated circuit (IS) single or multilayer metallization with the conductive layer 7 and the solid micromechanical structures from the same conductive Layer (7) are formed. Microsystem according to one of Claims 1, 3 to 7, in which Securing device against falling out of the freely movable Micromechanical structure are provided with the help at least one of the metallization levels is formed. Microsystem according to one of Claims 1 8, in which the conductive layer (7) or the conductive layers (2, 7) made of an aluminum alloy or essentially Tungsten exist and the insulating layer (5) or insulating layers (3, 5, 8) made of a silicon oxide exists or exist. Manufacturing method for a microsystem according to one of Claims 1 to 9, in which the fixed micromechanical structure is generated by structuring the conductive layer (7), which takes place simultaneously with the structuring of the conductive layer (7) in the region of the integrated circuit, at least a part of the intermediate space between the plates and the movable micromechanical structure is exposed in an etching process by removing an insulating layer (3, 5) which separates the fixed and the movable micromechanical structure, the etching process having sufficient selectivity to the conductive layer (7) and to the dielectric layer (4) and has an isotropic component. Manufacturing method according to claim 15, in which as an etching process a microwave-assisted isotropic dry etching is carried out. Manufacturing method according to claim 13, in which in the etching process a buffered RF solution is used. Manufacturing method according to one of claims 10 to 12, where the integrated circuit (IS) and the micromechanical Component (BT) with several conductive layers (2,7,) can be produced with additional insulating Layers (3,5,8) are covered, and in which the etching process the insulating layers with sufficient selectivity etches to the conductive layers.

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